AlGaAs/GaAs lasers have been manufactured commercially. But the lifetime of such lasers is limited severely by the presence of the AlGaAs material. The reason for the poor lifetime is attributed to the strong reactivity of aluminum (Al) with oxygen resulting in poor facet chemical stability and a decrease in the facet catastrophic optical damage limit. Also, the nearly equal size of Al and gallium (Ga) results in the easy generation and propagation of defects (dark lines defect and dark spot defects). The generation and propagation of dark line defect constitute a major failure mechanism for this type of laser. Consequently, the conventional wisdom dictates that Al be eliminated from laser structures.
GaInAsP/GaAs lasers have been developed to avoid the disadvantages attributed to the presence of Al. Such lasers have demonstrated far lower, long term degradation rates, higher power and the absence of sudden failure due to defect penning of Indium (In) atoms in GaInAsP. In lasers of this type GaInP is used as a cladding layer and large band gap GaInAsP is used as a waveguide material. But the band gap of GaInP is limited to 1.9 eV. Therefore, carrier leakage has been a major limiting factor. Also, GaInAsP used as the waveguide material, is nearly impossible to grade (linearly) in refractive index in order to achieve optimum wave guiding effects.
Since the limitations of the GaInAsP/GaAs structure could be overcome by the addition of Al, a contradiction results where Al is both to be eliminated and yet desired.